An electric dipole is placed in uniform electric field. The magnitude of electric dipole moment of dipole is p and external electric field intensity is E. Asume `theta` is the angle between electric dipole moment and electric field intensity and U represents potential energy of electric dipole

Options

A. If U=0 for `theta=0` then for other orientations `U=pE (1-cos theta)`
B. If U=0 for `theta=90^@` then for other orientations `U=-pE cos theta`
C. If U=0 for `theta=180^@` then for other orientations `U=-pE (1+cos theta)`
D. All of the above

Answer

A, B, C, D

Explanation

We write potential energy of electric dipole assuming potential energy equal to zero when the angle between electric dipole moment and electric field is `90^@` . In this case potential energy is written as `U=-pE cos theta` . Hence , option (b) is correct.
`U(theta)-U(0)=(-pE cos theta)-(-pE cos 0^@)`
`=pE (1-cos theta)`
Hence, option (a) is correct .
`U(theta)-U(180^@)=(-pE cos theta)-(-pE cos 180^@)`
`=-pE(1+cos theta)`
Hence , option (c) is correct.